Light emitting module having heat conductive substrate

ABSTRACT

A substrate having a plurality of light-emitting elements mounted thereon is described. The substrate may be mounted in a lighting apparatus and may include a surface on which the plurality of light-emitting elements are mounted and one or more holes through which heat may be conducted from the first surface to another surface of the substrate. For example, a heat conductive and electrically non-conductive material may cover a surface of the one or more holes. According to some arrangements, the surface of the substrate may include an electrically non-conductive layer and an electrically conductive layer such that the electrically non-conductive layer is electrically isolated or separated from the electrically conductive layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/665,227 filed Oct. 31, 2012, which is a continuation of U.S. patentapplication Ser. No. 12/473,447 filed May 28, 2009, issued as U.S. Pat.No. 8,556,460 on Oct. 15, 2013, which is based upon and claims thebenefit of priority from prior Japanese Patent Applications No.2008-142063, filed May 30, 2008; and No. 2009-071276, filed Mar. 24,2009. The entire contents of the above noted applications areincorporated herein by reference.

BACKGROUND

Aspects relate to a substrate having a plurality of light-emittingelements such as LEDs mounted thereon and to a lighting apparatus havingthis substrate incorporated in an apparatus main body.

Recently, lighting apparatus which uses a plurality of light-emittingelements such as LEDs as light sources have been developed. For lightingapparatus of this type, a demand of a high output is increasing, andthere is a tendency that the number of light-emitting elements employedis also increasing.

The plurality of light-emitting elements are mounted on the substrateand incorporated into an apparatus main body. The substrate is subjectedto heating and cooling by heat from the light sources as the lightingapparatus is turned on and off, and they repeatedly undergo thermalexpansion and thermal contraction. For this reason, the substrate iseasily warped or deformed due to heat.

Heretofore, to avoid such thermal deformation of the substrate, thesubstrate is pressed against the apparatus main body and both membersare fastened and fixed at a plurality of positions by using a pluralityof screws. As a result, tight connection of the substrate with respectto the apparatus main body can be improved, and heat of the substratecan be excellently conducted to the apparatus main body, thussuppressing warpage or deformation due to heat of the substrate.

However, when the substrate is screwed into the apparatus main body atthe plurality of positions as described above, the substrate getsdistorted and deformed when the substrate thermally expands andthermally shrinks between the fixing positions. When the substrate isdeformed in this manner, a soldered portion to which an electroniccomponent is secured may be cracked or the tight connection of thesubstrate with respect to the apparatus main body may be degraded insome cases. When the tight connection of the substrate is degraded, heatradiation of the substrate cannot be sufficiently performed, and thesubstrate is further deformed.

On the other hand, in the field of manufacture of a thinnedsemiconductor package, there is known a structure where a reinforcingmember is disposed to an upper side of a substrate to surround asemiconductor element mounted on the substrate and this- reinforcingmember is sealed together with the semiconductor element by a sealingmember in order to avoid warpage, breakage due to insufficiency ofstrength, a mounting error, and others.

However, in the structure depicted in this Patent Document, when linearexpansion coefficients of the substrate, the reinforcing member, and thesealing member are different from each other, warpage or deformationoccurs in the substrate increasingly. Therefore, selecting materials forthe respective members is difficult. Further, since the reinforcingmember must be prepared separately from the substrate, the number ofcomponents is increased, and the number of manufacturing steps is alsoincreased.

If the reinforcing structure disclosed in this Patent Document isadopted for the substrate in the lighting apparatus having the pluralityof light-emitting elements mounted thereon, thermal deformation of thesubstrate cannot be effectively avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a perspective view showing a down light according to a firstembodiment of a lighting apparatus of the present invention;

FIG. 2 is a view showing a substrate incorporated in the down light inFIG. 1 as seen from a front surface side thereof;

FIG. 3 is a partially enlarged cross-sectional view showing thesubstrate in FIG. 2 taken along a line III-III;

FIG. 4 is a view showing a reflector incorporated in the down light inFIG. 1 as seen from the front surface side thereof;

FIG. 5 is a cross-sectional view of the reflector in FIG. 4 taken alonga line V-V;

FIG. 6 is a partially enlarged cross-sectional view showing a primarypart of the down light in FIG. 1 in a partially enlarged manner;

FIG. 7 is a view showing a substrate according to a second embodiment ofthe present invention as seen from a front surface side thereof;

FIG. 8 is a view showing a substrate according to a third embodiment ofthe present invention as seen from a front surface side thereof;

FIG. 9 is a view showing a substrate according to a fourth embodiment ofthe present invention as seen from a front surface side thereof;

FIG. 10 is a view showing a substrate according to a fifth embodiment ofthe present invention as seen from a front surface side thereof;

FIG. 11 is a view showing a substrate according to a sixth embodiment ofthe present invention as seen from a front surface side thereof; and

FIG. 12 is a partially enlarged cross-sectional view showing thesubstrate in FIG. 11 cut at positions of via holes.

DETAILED DESCRIPTION

Aspects described herein relate to providing a lighting apparatus whichcan suppress thermal deformation of a substrate having a plurality oflight-emitting elements mounted thereon and demonstrate stableperformance for a long time, and a substrate incorporated in thislighting apparatus.

For example, a substrate according to an embodiment may comprise a frontsurface on which a plurality of light-emitting elements are mounted; aplurality of mounting portions which are used for attachment to alighting apparatus; and stress absorbing means arranged on imaginarystraight lines connecting the plurality of mounting portions with eachother.

Additionally or alternatively, a lighting apparatus according to anembodiment may comprise an apparatus main body; and the above substratewhich is mounted on the apparatus main body.

According to other aspects, a lighting apparatus may include athermally-conductive apparatus main body; and a substrate which is fixedto the apparatus main body through a plurality of fixing means, has aplurality of light-emitting elements mounted thereon, and has slitswhich are provided on imaginary straight lines connecting the pluralityof fixing means with each other and extended in directions orthogonal tothe straight lines.

A substrate may include a plurality of light-emitting elements mountedthereon and may be incorporated in a lighting apparatus. The substratemay also include stress absorbing means for taking out stress caused dueto thermal deformation of the substrate between a plurality of fixingmeans for fixing the substrate at a plurality of positions with respectto a fixing member of the lighting apparatus.

A substrate and lighting apparatus according to the first embodiment ofthe present invention will be described with reference to FIGS. 1 to 6.As an example of the lighting apparatus, the case where the presentinvention is applied to a down light 1 will be discussed.

FIG. 1 is a perspective view of the down light 1, FIG. 2 is a viewshowing a substrate 4 incorporated in the down light 1 as seen from afront surface side thereof, FIG. 3 is a partially enlargedcross-sectional view showing the substrate 4 in FIG. 2 taken along aline III-III, FIG. 4 is a view showing a reflector 6 incorporated in thedown light 1 in FIG. 1 as seen from the front surface side thereof, FIG.5 is a cross-sectional view of the reflector 6 in FIG. 4 taken along aline V-V, and FIG. 6 is a partially enlarged cross-sectional viewshowing a primary part of the down light 1 in FIG. 1 in a partiallyenlarged manner.

As light-emitting elements serving as the light source of the down light1, solid-state light-emitting elements such as light-emitting diode(LED) and organic electro-luminescence (organic EL) are considered. Itis preferable that the light-emitting element is mounted on a substrateby the chip-on-board method or surface mounting method; however thepresent invention is not limited to these mounting methods. Further, thenumber of light-emitting elements can be set arbitrarily. In each of thefollowing embodiments, the case where an LED 10 is employed as alight-emitting element will be discussed.

FIG. 1 is a perspective view of the down light 1 of the ceiling built-intype. The down light 1 includes a cylindrical main body 2, a decorativeframe 3, a substrate 4, a power unit 5, a reflector 6, a lighttransmitting cover 7, a terminal block 8 and a pair of mounting leafsprings 9. The substrate 4 and power unit 5 are housed within thecylindrical main body 2.

The cylindrical main body 2 is formed of an aluminum die casting, whichhas a relatively high thermal conductivity. Besides this, it is possiblethat the cylindrical main body 2 is formed of some other material whichhas a high thermal conductivity. An outer circumferential surface of thecylindrical main body 2 is provided a plurality of heat releasing fins 2c each extending in an axial direction. Further, the outercircumferential surface is subjected to baking finishing with awhite-color melanin resin-based paint. The terminal block 8 to beconnected to a utility power is mounted to the outer circumferentialsurface of the cylindrical main body 2.

The decorative frame 3 is mounted to the lower end of the cylindricalmain body 2. The decorative frame 3 is formed of an ABS resin. Thedecorative frame 3 is formed into an umbrella shape which widensdownwards from the end of the cylindrical main body 2 where the frame ismounted, and an annular-shaped flange 3 a is formed on the opening endwhere the frame is widened at maximum. Further, a pair of mounting leafsprings 9 are placed on an inclining outer surface of the decorativeframe 3.

As shown in FIG. 2, a plurality of (twelve in this embodiment) LEDs 10are mounted on the substrate 4. The substrate 4 is placed in a spacebetween the bottom wall 2 a of the cylindrical main body 2 and thedecorative frame 3 described above, as shown in FIG. 6. In more detail,the rear surface of the substrate 4 is brought into contact with thelower surface of the bottom wall 2 a of the cylindrical main body 2, andthe rear surface of the reflector 6 is brought into contact with thesurface side of the substrate 4. Then, the decorative frame 3 is mountedto the surface side of the reflector 6 while interposing the lighttransmitting cover 7 therebetween.

As shown in FIG. 3, the substrate 4 has a base plate 40 formed of aglass epoxy resin, a wiring pattern layer 41 formed on a front surfaceside of this base plate 40, a resist layer (not shown) appropriatelyprovided on this wiring pattern layer 41, and a heat radiation layer 42formed on a back surface side of the base plate 40. The wiring patternlayer 41 is formed of a material having electrical conductivity, e.g., acopper foil in order to supply electric power to the plurality of LEDs10 from a power supply.

The LED 10 is a surface-mount type LED package and soldered to a frontsurface side of the substrate 4. The LED package is roughly constitutedof a main body 10 a formed of resin, an LED chip mounted on this mainbody 10 a, and a translucent resin for molding, e.g., an epoxy-basedresin or a silicone-based resin that seals this LED chip. In thistranslucent resin, a fluorescent substance which absorbs luminescence ofthe LED chip and generates yellowish light is dispersed. Further, a pairof terminals, i.e., an anode terminal 10 b and a cathode terminal 10 cwhich are connected with the LED chip are extended from the main body 10a in a plane direction, and the anode terminal 10 b and the cathodeterminal 10 c are electrically connected with the wiring pattern layer41.

The power unit 5 has the structure in which electronic parts such ascontroller-use ICs, transformers, capacitors and the like are mounted ona circuit board, which is not shown in the figure. The power unit 5controls the lighting of the LEDs 10 by its lighting circuits. Further,the power unit 5 is electrically connected to the terminal block 8.

The reflector 6 shown in FIG. 4 has a substantially columnar externalshape having a relatively short dimension in its axial direction, and itis made of, for example, a white color polycarbonate or an ABS resin.The reflector 6 is placed on the front surface side of the substrate 4,that is, on the lighting side of the LEDs 10, so as to perform luminousintensity distribution control which guide the light emitted from eachof the LEDs 10 in its respectively desired direction at a desiredintensity.

This reflector 6 contains twelve round floodlight openings 6 a on therear surface side thereof, which is brought into contact with thesubstrate 4. The twelve round floodlight openings 6 a expose the twelveLEDs 10 mounted on the substrate 4, respectively, to the front surfaceof the reflector 6. Further, the reflector 6 includes an annular-shapedouter peripheral portion 6 b on its outer circumference. The outerperipheral portion 6 b functions as one of partition walls, which has aheight substantially the same as the axial length of the reflector 6.

Within the outer peripheral portion 6 b, twelve reflection concavesurfaces 6 f are formed in the front surface side of the reflector 6 soas to correspond to the twelve round floodlight openings 6 a,respectively. Each of the twelve reflection concave surfaces 6 f ispartitioned by a plurality of partition walls 6 c, 6 d and 6 e eachhaving an angle shape in cross section. These plurality of partitionwalls 6 c, 6 d and 6 e each have a height substantially the same as theaxial length of the reflector 6 as well. Each of the reflection concavesurfaces 6 f has such a shape that it opens wider on the front surfaceside of the reflector 6 from the floodlight opening 6 a at its bottomportion towards the ridge line of each of the surrounding partitionwalls 6 c, 6 d and 6 e. More specifically, each of the reflectionconcave surfaces 6 f has such a shape of substantially a bowl, whosecross section is as shown in FIGS. 5 and 6.

In more detail, on the front surface side of the reflector 6, threeradial partition walls 6 c radially extending from its central portiontowards the outer peripheral portion 6 b are formed. The three radialpartition walls 6 c are arranged at intervals of about 120 degrees fromeach other. Further, within the outer peripheral portion 6 b, a roundinner circumferential partition wall 6 d is formed such as to divideeach of the radial partition walls 6 c into two. Furthermore, twodividing partition walls 6 e are formed in a radial arrangement from anouter wall of the inner circumferential partition wall 6 d located inthe middle of each of the radial partition walls 6 c towards the outercircumferential portion 6 b (a total of six dividing partition walls 6e). Each of the plurality of types of partition walls 6 b, 6 c, 6 d and6 e is formed to have an angle shape in its cross section as seen inFIGS. 5 and 6.

That is, within the round inner circumferential partition wall 6 d,three reflection concave surfaces 6 f each having substantially a fanshape, which are partitioned by the three radial partition walls 6 c,are formed. Further, within the outer circumferential portion 6 b butoutside of the inner circumferential partition wall 6 d, nine reflectionconcave surfaces 6 f each having substantially a trapezoidal shape,which are partitioned by the three radial partition walls 6 c and thesix dividing partition walls 6 e, are formed. Furthermore, at the bottomof each of a total of twelve reflection concave surfaces 6 f, afloodlight opening 6 a is formed to expose the respective LED 10.

For example, the three reflection concave surfaces 6 f each havingsubstantially a fan shape inside the inner circumferential partitionwall 6 d, are surrounded respectively by the ridge line of the innercircumferential partition wall 6 d and the ridge lines of the radialpartition walls 6 c. On the other hand, the nine reflection concavesurfaces 6 f each having substantially a trapezoidal shape, in theoutside of the inner circumferential partition wall 6 d are surroundedrespectively by the ridge line of the outer circumferential portion 6 b,the ridge lines of the radial partition walls 6 c, the ridge line of theinner circumferential partition wall 6 d and the ridge lines of thedividing partition walls 6 e.

When the twelve LEDs 10 of the down light 1 having the above-describedstructure are turned on, light emitted from each of the LEDs 10 passesthrough the light transmitting cover 7 directly and also reflects on theabove-described twelve reflection concave surfaces 6 f of the reflectorand the reflection light passes through the light transmitting cover 7as well. Here, when the twelve reflection concave surfaces 6 f aredesigned to have an appropriate shape, the distribution of the lightemitted from each of the LEDs 10 can be controlled. Thus, it becomespossible to perform highly efficient luminous intensity distributioncontrol in the down light 1 as a whole.

As shown in FIG. 2, a plurality of LEDs 10 are mounted on the frontsurface side of the substrate 4 by the surface mounting method, and morespecifically, a total of twelve of them, three are placed near thecentral portion and nine are placed around them. These twelve LEDs 10are placed at positions corresponding to the above-described twelvefloodlight openings 6 a of the reflector 6.

The substrate 4 is made of an insulation material or a metal-madesubstantially round disk, and has a screw through hole 4 a at its centerand three screw through holes 4 b, 4 c and 4 d near the peripheralportion thereof arranged at intervals of 120 degrees from each other. Itis to be noted that a slit 4 s is formed between the central screwthrough hole 4 a and each of the screw through holes 4 b, 4 c and 4 daround the central screw through hole 4 a, and each slit 4 s functionsas stress absorbing means of the present invention which absorbsexpansion and contraction caused by the thermal expansion of thesubstrate 4.

Each of these three slits 4 s is formed into an arched shape around thescrew through hole 4 a at the center of the substrate 4, and provided onan imaginary straight line connecting the central screw through hole 4 awith the peripheral screw through hole 4 b, 4 c or 4 d. In thisembodiment, although the three slits 4 s are provided as the stressabsorbing means between the central hole 4 a and the peripheral holes 4b, 4 c and 4 d in this embodiment, slits which are extended in a radialpattern from the center of the substrate 4 may be formed between theperipheral holes 4 b, 4 c and 4 d in addition to these slits 4 s.

In the case where this substrate 4 is to be formed of an insulatingmaterial, it is desirable that a ceramic material or a synthetic resinmaterial, which has a relatively good heat radiating property and anexcellent durability, is employed. In the case where the substrate 4 isto be formed of a synthetic resin material, it is desirable that, forexample, a glass epoxy resin or the like is employed. Alternatively, inthe case where the substrate 4 is to be formed of a metal, it issuitable to employ a material having a good thermal conductivity and anexcellent heat radiating property, such as aluminum.

Here, a mounting structure of the above down light 1 will be described.

As can be seen in FIG. 6 (in which the illustration of the mounting leafspring 9 is omitted), the substrate 4 is placed on the bottom wall 2 aof the cylindrical main body 2 such that the rear surface of thesubstrate 4 is brought into contact by surface thereto. Further, thereflector 6 is placed on the front surface side of the substrate 4 suchthat the rear surface of the reflector 6 is brought into contacttherewith. In other words, the substrate 4 is sandwiched between thebottom wall 2 a of the cylindrical main body 2 and the reflector 6.

When the substrate 4 and reflector 6 are to be mounted to the bottomwall 2 a, the substrate 4 is first secured to the bottom wall 2 a (amember to which it is secured). During this process, the mounting screw11 which functions as securing means of the present invention is putthrough the central screw through hole 4 a from the front surface sideof the substrate 4, and then screwed into a threaded hole of the bottomwall 2 a, thereby securing the substrate 4 to the bottom wall 2 a byengagement. The securing position of the substrate 4 by the mountingscrew 11, i.e., the portion of the central screw through hole 4 afunctions as the mounting portion of the present invention.

Then, the reflector 6 is placed on top of the front surface side of thesubstrate 4 such that the twelve LEDs 10 mounted on the surface of thesubstrate 4 are respectively located within the corresponding twelvefloodlight openings 6 a.

While maintaining this state, three mounting screws 12 which function asthe securing means of the present invention (only two of them areillustrated and one of the two is illustrated with an imaginary line)are put through the screw through hole of the bottom wall 2 a and thescrew through holes 4 b, 4 c and 4 d of the substrate 4, respectively,from the rear surface side of the bottom wall 2 a of the cylindricalmain body 2, and they are screwed into threaded holes 6 g formed in therear surface side of the reflector 6. The three threaded holes 6 g ofthe reflector 6 are provided on the rear surface side of the reflector 6at positions which over-lap with the radial partition walls 6 c as shownin FIGS. 4 and 5. It is to be noted that the portions of these screwthrough holes 4 b, 4 c and 4 d also function as the mounting portions ofthe present invention.

While maintaining this state, as the three mounting screws 12 arefastened, the fastening force acts in the direction in which thereflector 6 is pulled towards the bottom wall 2 a. Thus, the fasteningforces for the mounting screw 11 at the central portion of the substrate4 and the surrounding mounting screws 12 synergistically act together totightly fasten the rear surface of the substrate 4 onto the frontsurface of the bottom wall 2 a. At this time, the reflector 6 is alsopushed onto the front surface side of the substrate 4, thereby enhancingthe tight connection between both the members.

In particular, at fastening positions (mounting portions) of themounting screws 11 and 12, the substrate 4 is tightly fastened onto thebottom wall 2 a of the cylindrical main body 2, whereby these membersare strongly fixed to each other. On the other hand, at portions otherthan the fastening positions, the substrate 4 can slightly move in aplane direction with respect to the bottom wall 2 a. That is, when thesubstrate 4 thermally expands or thermally shrinks, the portions otherthan the fastening positions thermally expand or thermally contract inthe plane direction.

After that, the decorative frame 3 is mounted to the cylindrical mainbody 2 by the mounting screw 13. Then, as the down light 1 is built in aceiling surface C as shown in FIG. 6, the flange 3 a which has adiameter larger than that of the embedding hole of the ceiling surface Cis hooked at the periphery of the embedding hole from the lower sidethereof. It is to be noted that the inner circumferential side of thedecorative frame 3 is provided with the light transmitting cover 7 madeof an acryl resin or the like so as to cover the opening of the frontsurface side of each of the twelve reflection concave surfaces 6 f ofthe reflector 6.

Here, the heat radiating structure when the down light 1 having theabove-described structure is turned on, and the thermal deformation ofthe substrate 4 will now be discussed.

When the power unit 5 is energized, the lighting circuit is driven tosupply electric power to the substrate 4, and thus the twelve LEDs 10emit light. Much of the light emitted from each of the LEDs 10 transmitsthe light transmitting cover 7 directly and irradiates forwards. Aportion of the light reflects on each of the reflection concave surfaces6 f of the reflector 6 and the reflection light is subjected to luminousintensity distribution control. Then, the reflection light passesthrough the light transmitting cover 7 and irradiates forwards as well.

On the other hand, the heat generated from each of the LEDs 10propagates mainly from the rear surface of the substrate 4 to the bottomwall 2 a of the cylindrical main body 2. Further, while being radiatedin its propagation process, the heat propagates to the entire body ofthe cylindrical main body 2, and then radiated through the plurality ofheat radiating fins 2 c. At this time, needless to say, the substrate 4is heated and thermally expanded most. When the LEDs 10 are turned off,the thermally expanded substrate 4 is naturally cooled and shrinks tothe original size. That is, thermal expansion and thermal shrinkage ofthe substrate 4 are repeated by repeating turning on/off the LEDs 10.

In particular, when the substrate 4 is made of a resin having a higherthermal expansion coefficient than that of the cylindrical main body 2formed by die-casting using aluminum, the substrate 4 thermally expandswith the portions where the substrate 4 is fastened and fixed to thebottom wall 2 a of the cylindrical main body 2 (the portions of the fourscrew through holes 4 a, 4 b, 4 c and 4 d in this embodiment) (whichwill hereinafter simply be referred to as fixing portions 4 a, 4 b, 4 cand 4 d sometimes) at the center, stress is concentrated on portionsbetween the plurality of fixing portions, and warpage or deformationoccurs in the substrate 4 in these intermediate portions. However, sincethe substrate 4 according to this embodiment has the three slits 4 s,stress caused due to thermal expansion can be taken out, thus avoidingwarpage or deformation of the substrate 4.

It is to be noted that the three slits 4 s in the substrate 4 candemonstrate effects even in a reflow process in a manufacturing processof the substrate 4. That is, the plurality of slits 4 s suppressdeformation of the substrate 4 due to thermal expansion even in themanufacturing process of the substrate 4.

Further, when the substrate 4 is fastened and fixed to the cylindricalmain body 2 with the four fixing portions 4 a, 4 b, 4 c and 4 ddescribed above, the tight connection of the substrate 4 to the bottomwall 2 a is reliably maintained, thereby making it possible to radiateheat effectively from the substrate 4 to the cylindrical main body 2 andsuppress the deformation of the substrate 4 as well. Moreover, the rearsurface of the reflector 6 is brought into contact with the frontsurface of the substrate 4 over the substantially entire area thereof,and thus the tightness is assured by this way as well. Therefore, due tothe heat conduction from the substrate 4 to the reflector 6, it ispossible to prevent a regional temperature increase in the substrate 4and uniform the temperature distribution of the substrate 4. In thismanner, the temperatures of the plurality of LEDs 10 can be uniformed.When the temperature of the substrate 4 can be homogenized in thismanner, temperatures of the plurality of lighted LEDs 10 becomeconstant, and unevenness of color, brightness, life duration, and otherscan be reduced, thereby demonstrating stable excellent performance for along time.

As described above, in the down light 1 of this embodiment, the numberof LEDs 10 mounted on the substrate 4 can be increased, and therefore itis possible to meet the demand of a higher output. Further, in thesubstrate 4 of this embodiment, the deformation thereof due to heat canbe suppressed, and therefore it is possible to prevent defects as cracksin solder portions of the mounted electronic parts. Moreover, accordingto this embodiment, the tight attachment of the substrate 4 onto thecylindrical main body 2 can be assured, and therefore the heat radiationcan be effectively performed and the deformation of the substrate 4 canalso be prevented. Therefore, according to the down light 1 of thisembodiment, the plurality of LEDs 10 can emit light under the sameconditions, and hence stable performance can be exercised for a longtime.

Next, a substrate 401 according to a second embodiment of the presentinvention will now be described with reference to FIG. 7. FIG. 7 is aview showing the substrate 401 from a front surface side and correspondsto FIG. 2 in the explanation of the first embodiment. Here, likereference numerals denote parts equal to or corresponding to those inthe first embodiment, thereby omitting a tautological explanation.

A method of mounting the substrate 401 onto a cylindrical main body 2 inthis embodiment is different from that in the first embodiment. That is,in this embodiment, mounting screws 11 and 12 are inserted into andfastened to a bottom wall 2 a of the cylindrical main boy 2 from thefront surface side of the substrate 4 to fasten and fix the substrate401 onto the bottom wall 2 a of the cylindrical main body 2. A basicstructure of the substrate 401 is the same as that in the firstembodiment.

In this embodiment, since slits 4 s are likewise formed as stressabsorbing means between the mounting screw 11 and the three mountingscrews 12, concentration of stress caused due to thermal expansion ofthe substrate 401 can be avoided, and a mounting state of the substrate401 can be stably maintained like the first embodiment. Furthermore,tight connection with respect to the cylindrical main body 2 can beenhanced, and deformation of the substrate 401 can be suppressed, thusmaintaining the tight connection of the substrate 401 to the cylindricalmain body 2.

Moreover, adopting the method of mounting the substrate 401 according tothis embodiment enables inserting and fastening the mounting screws 11and 12 from the front surface side of the substrate 401, and assemblingworkability of a down light 1 can be improved. The respective mountingscrews 11 and 12 can be securely fastened, and the tight connection ofthe substrate 401 to the bottom wall 2 a of the cylindrical main body 2can be further improved.

A substrate 402 according to a third embodiment of the present inventionwill now be described with reference to FIG. 8. FIG. 8 is a view showingthe substrate 402 from a front surface side and corresponds to FIGS. 2and 7 of the respective embodiments. In this example, like referencenumerals likewise denote constituent elements having the same functionsas those in the foregoing embodiments, thereby omitting a detailedexplanation thereof.

The substrate according to this embodiment is different from those ofthe foregoing embodiments in that a screw through hole 4 a at a centralportion of the substrate 402 is omitted and three slits 4 s-3 havingdifferent shape and directions are provided. That is, each of the slits4 s-3 is provided at a substantially central part of each side of animaginary regular triangle connecting three screw through holes 4 b, 4 cand 4 d formed in the substrate 402 in such a manner that each slitbecomes substantially orthogonal to each side.

In this embodiment, since the slits 4 s-3 are provided between thefixing portions 4 b, 4 c and 4 d of the substrate 402, the same effectsas those in the respective foregoing embodiments can be exercised, andconcentration of stress caused due to thermal expansion of the substrate402 can be avoided, thereby suppressing warpage or deformation of thesubstrate.

Moreover, according to this embodiment, since the screw through hole 4 aat the center of the substrate 402 is omitted and directions of theslits 4 s-3 are changed to a radial pattern extending from the center ofthe substrate 402, a reduction in strength due to formation of the slitsor the screw holes in the substrate 402 can be suppressed. Additionally,since the screw through hole 4 a at the center is omitted, the number ofmanufacturing steps of the substrate 402 can be decreased.

FIG. 9 is a view showing a substrate 403 according to a fourthembodiment of the present invention from a front surface side. In thisembodiment, screw through holes 4 b, 4 c, 4 d and 4 e are formed at fourpositions in a peripheral portion of the substrate 403 at equalintervals, and each of substantially rectangular slits 4 s-4 is formedon each side of an imaginary square connecting these four holes. It isto be noted that, although not shown, a slit may be formed on eachdiagonal line connecting the screw through holes 4 b and 4 d or thescrew through holes 4 c and 4 e.

In this embodiment, the same effects as those in the foregoingembodiments can be demonstrated, and concentration of stress caused dueto thermal expansion of the substrate 403 can be avoided, wherebywarpage or deformation of the substrate 403 can be suppressed.

FIG. 10 is a view showing a substrate 404 according to a fifthembodiment of the present invention from a front surface side. Thesubstrate 404 according to this embodiment has substantially the samestructure as that of the substrate 4 according to the first embodimentexcept that three circular holes 4 s-5 are formed in place of the threearched slits 4 s. Therefore, here, like reference numerals denoteconstituent elements having the same functions as those in the firstembodiment, thereby omitting a detailed explanation thereof.

In this embodiment, the same effects as those in the respectiveforegoing embodiments can be exercised, and concentration of stresscaused due to thermal expansion of the substrate 404 can be avoided,whereby deformation and deformation of the substrate can be suppressed.

FIG. 11 is a view showing a substrate 405 according to a sixthembodiment of the present invention from a front surface side. Further,FIG. 12 is a partially enlarged cross-sectional view in which thesubstrate 405 is cut at positions of via holes 4 v. In this embodiment,so-called via holes 4 v are formed as stress absorbing means in thesubstrate 405. It is to be noted that the substrate 405 according tothis embodiment has the same structure as that in the first embodimentexcept that the plurality of via holes 4 v are provided in place of thearched slits 4 s, and hence like reference numerals denote constituentelements that function in the same manner as the first embodiment,thereby omitting a detailed explanation thereof.

As shown in FIG. 11, the via holes 4 v constituted of many small holesare formed as the stress absorbing means according to the presentinvention in the substrate 405. The plurality of via holes 4 v arearranged at least between a screw through hole 4 a at a central portionas a fixing portion and screw through holes 4 b, 4 c and 4 d at aperiphery. Further, the via holes 4 v may be formed on respective sidesof an imaginary triangle having the peripheral screw through holes 4 b,4 c and 4 d as apexes.

As shown in FIG. 12, a wiring pattern layer 41 formed on a front surfaceside of the substrate 405 is formed of a material having electricalconductivity, e.g., a copper foil in order to supply electric power froma power supply to a plurality of LEDs 10. In this embodiment, thiswiring pattern layer 41 is constituted of a conductive layer 41 a whichactually supplies electric power to electronic components, e.g., theLEDs 10 and a non-conducting layer 41 b which is not electricallyconnected with electronic components and through which electric power isnot conducted.

This non-conducting layer 41 b is formed on the front surface side ofthe substrate 405 and has a function of radiating heat of the substrate405 and homogenizing a temperature on the front surface of the substrate405. On the other hand, a heat radiation layer 42 formed on a backsurface side of the substrate 405 is made of a material having excellentheat conductivity, e.g., a copper foil. Furthermore, the plurality ofvia holes 4 v are formed by performing copper plating processing withrespect to an inner peripheral surface of each through hole pierced fromthe non-conducting layer 41 b to the heat radiation layer 42.

Therefore, although the plurality of via holes 4 v do not electricallyconnect the layers on the front and back surface sides of the substrate405, i.e., the non-conducting layer 41 b and the heat radiation layer 42with each other, they connect the layers 41 b and 42 on the front andback surface sides of the substrate 405 with each other to achieve heatconduction for heat radiation and temperature homogenization.

That is, heat generated from the plurality of LEDs 10 mounted on thefront surface side of the substrate 405 is conducted to the wiringpattern layer 41 (the conductive layer 41 a and the non-conducting layer41 b) and transferred to the heat radiation layer 42 through theplurality of via holes 4 v connected with the non-conducting layer 41 b.Moreover, the heat of the substrate 405 is conducted to a cylindricalmain body 2 through the heat radiation layer 42 which is insurface-contact with a bottom wall 2 a of the cylindrical main body 2and radiated through a plurality of radiation fins 2 c.

As explained above, according to this embodiment, heat of the LEDs 10can be effectively conducted from the non-conducting layer 41 b to theheat radiation layer 42 through the plurality of via holes 4 v, andappropriately setting the number or positions of the via holes 4 venables homogenizing a temperature in a temperature distribution on thefront surface of the substrate 405. That is, the plurality of via holes4 v function as stress absorbing means to avoid thermal deformation ofthe substrate 405 and function as heat transferring means to contributeto homogenizing a temperature of the substrate 405, i.e., homogenizingtemperatures of the plurality of LEDs 10.

That is, although the substrate 405 expands due to heat generated fromthe plurality of LEDs 10, since the plurality of via holes 4 v arepresent between the central screw through hole 4 a and the peripheralscrew through holes 4 b, 4 c and 4 d as fixing portions, stress causeddue to thermal expansion can be absorbed by the plurality of via holes 4v, thereby suppressing warpage or deformation of the substrate 405.

It is to be noted that arranging the plurality of via holes 4 v to bepresent at least between the fixing portions can suffice. Specificarrangement positions or number of the via holes 4 v can beappropriately selected while considering heat radiation characteristicsof a down light 1 or the substrate 405 or a degree of absorption ofthermal expansion of the substrate 405.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

For example, although the slits or the holes are simply formed in thesubstrate 4 as the stress absorbing means to avoid concentration ofstress caused due to thermal deformation in the respective foregoingembodiments, the slits or the holes may be filled with a differentmaterial, e.g., an elastic member to avoid concentration of stresscaused due to thermal expansion.

Additionally, the via holes 4 v formed in the substrate 4 in the sixthembodiment described with reference to FIGS. 11 and 12 may be formed inthe substrate 4 in each of the first to fifth embodiments, and the sameeffects as those in the sixth embodiment can be thereby demonstrated. Inthis case, if the substrate 4 according to the first embodiment is used,a copper foil can be formed on an inner peripheral surface of each slit4 s to connect the front and back surfaces of the substrate 4 with eachother.

Further, although the structure where the substrate 4 is fixed to thebottom wall 2 a of the apparatus main body 2 as a fixing member on thelighting apparatus 1 side to which the substrate 4 is disposed has beenexplained in the foregoing embodiments, the present invention is notrestricted thereto, and the substrate 4 may be fixed to, e.g., aso-called main body, a case, a cover, or a heat radiation member as thefixing member that is used to fix the substrate 4.

Furthermore, although the structure where the slits or the holes as thestress absorbing means are arranged on imaginary straight linesconnecting the plurality of mounting portions of the substrate 4 hasbeen explained in the foregoing embodiments, the stress absorbing meansdo not have be necessarily provided between all the mounting portions,and the number or positions of the stress absorbing means can beappropriately set in accordance with heat-resisting properties requiredfor the lighting apparatus 1 to which the present invention is applied.

What is claimed is:
 1. A module substrate comprising: a substratecomprising a first surface and a second surface opposite to the firstsurface; a light-emitting element mounted on the first surface; anelectrically conducting layer on the first surface, wherein theelectrically conducting layer is connected to the light-emittingelement; and a heat-conductive hole comprising a through hole extendingentirely through the substrate between the first surface and the secondsurface and a heat-conductive material covering an inner surface of thethrough hole, wherein the material covering the inner surface of thethrough hole is not electrically connected to the electricallyconducting layer.
 2. A lighting apparatus comprising: an apparatus mainbody; and a module substrate, the module substrate comprising: asubstrate comprising a first surface and a second surface opposite tothe first surface; a light-emitting element mounted on the firstsurface; an electrically conducting layer on the first surface, whereinthe electrically conducting layer is connected to the light-emittingelement; and a heat-conductive hole comprising a through hole extendingentirely through the substrate between the first surface and the secondsurface and a heat-conductive material covering an inner surface of thethrough hole, wherein the material covering the inner surface of thethrough hole is not electrically connected to the electricallyconducting layer.